U.S. patent number 5,759,917 [Application Number 08/774,488] was granted by the patent office on 1998-06-02 for composition for oxide cmp.
This patent grant is currently assigned to Cabot Corporation. Invention is credited to Gautam S. Grover, Brian L. Mueller.
United States Patent |
5,759,917 |
Grover , et al. |
June 2, 1998 |
Composition for oxide CMP
Abstract
A chemical mechanical polishing composition comprising
carboxylic acid, a salt and a soluble cerium compound at a pH above
3 and a method to selectively polish a silicon oxide overfill in
preference to a silicon nitride film layer in a single step during
the manufacture of integrated circuits and semiconductors.
Inventors: |
Grover; Gautam S. (Lisle,
IL), Mueller; Brian L. (Aurora, IL) |
Assignee: |
Cabot Corporation (Boston,
MA)
|
Family
ID: |
25101406 |
Appl.
No.: |
08/774,488 |
Filed: |
December 30, 1996 |
Current U.S.
Class: |
438/690; 106/11;
51/309; 438/692; 438/693 |
Current CPC
Class: |
C09K
3/1463 (20130101); H01L 21/31053 (20130101); C09G
1/02 (20130101) |
Current International
Class: |
C23F
1/00 (20060101); C09K 3/14 (20060101); C09G
1/00 (20060101); C09G 1/02 (20060101); H01L
21/3105 (20060101); H01L 21/02 (20060101); H01L
21/304 (20060101); H01L 21/302 (20060101); C03C
025/06 (); C23F 001/00 () |
Field of
Search: |
;106/3,11 ;51/306,309
;156/653.1,654.1 ;252/79.1 ;438/690,692,693 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
NYACOI Colloidal Ceria Nitrate MSDS (Oct. 17, 1994)..
|
Primary Examiner: Jones; Deborah
Claims
What we claim is:
1. An aqueous chemical mechanical polishing composition
comprising:
a salt;
soluble cerium; and
a carboxylic acid, wherein the composition has a pH of from about 3
to about 11.
2. The aqueous chemical mechanical polishing composition of claim
1, wherein the pH is from about 3.8 to about 5.5.
3. The aqueous chemical mechanical polishing composition of claim
1, wherein the salt is a nitrate salt.
4. The aqueous chemical mechanical polishing composition of claim
3, wherein the nitrate salt is a compound having the formula:
wherein n and m are both integers and wherein when n=m, M is an
alkali earth metal, H, NH.sub.4 or NR.sub.4 where R is an alkyl
group having from 1 to 10 carbon atoms and wherein when n.noteq.m,
M is a multivalent cation or metal or a combination of multivalent
cations and monovalent cations.
5. The aqueous chemical mechanical polishing composition of claim
3, including from about 0.05 to about 6.0 weight percent nitrate
salt.
6. The aqueous chemical mechanical polishing composition of claim
3, wherein the nitrate salt is ammonium cerium nitrate.
7. The aqueous chemical mechanical polishing composition of claim
1, wherein the carboxylic acid is selected from the group
consisting of monofunctional acids, di-functional acids and salts
thereof.
8. The aqueous chemical mechanical polishing composition of claim
1, wherein the carboxylic acid is at least one compound selected
from the group consisting of acetic acid, adipic acid, butyric
acid, capric acid, caproic acid, caprylic acid, citric acid,
glucaric acid, glycolic acid, formic acid, fumaric acid, lactic
acid, lauric acid, malic acid, maleic acid, malonic acid, myristic
acid, oxalic acid, palmitic acid, phthalic acid, propionic acid,
pyruvic acid, stearic acid, succinc acid, tartaric acid, valeric
acid, 2-(2-methoxyethoxy) acetic acid,
2-[2-(2-methoxyethoxy)ethoxy] acetic acid and poly(ethylene
glycol)bis (carboxymethyl)ether and mixtures thereof.
9. The aqueous chemical mechanical polishing composition of claim
1, wherein the carboxylic acid is acetic acid.
10. The aqueous chemical mechanical polishing composition of claim
1 including from about 0.05 to about 10.0 weight percent carboxylic
acid.
11. The aqueous chemical mechanical polishing composition of claim
10, including from about 0.1 to about 3.0 weight percent carboxylic
acid.
12. The aqueous chemical mechanical polishing composition of claim
1, including from about 0.05 to about 10 weight percent soluble
cerium.
13. The aqueous chemical mechanical polishing composition of claim
1, wherein the soluble cerium is at least one compound selected
from the group consisting of ammonium cerium sulfate, cerium
acetate, cerium sulfate hydrate, cerium hydroxide, cerium bromate,
cerium bromide, cerium chloride, cerium oxalate, cerium nitrate,
cerium carbonate and mixtures thereof.
14. The aqueous chemical mechanical polishing composition of claim
1, wherein the salt and the soluble cerium are ammonium cerium
nitrate.
15. The aqueous chemical mechanical polishing composition of claim
14, including from about 0.1 to about 4.0 weight percent ammonium
cerium nitrate.
16. A chemical mechanical polishing slurry comprising:
a salt;
soluble cerium;
a carboxylic acid; and
an abrasive, wherein the composition has a pH of from about 3 to
about 11.
17. The chemical mechanical polishing slurry of claim 16, including
from about 1 to about 25 weight percent abrasive.
18. The chemical mechanical polishing slurry of claim 16, wherein
the abrasive is a metal oxide.
19. The chemical mechanical polishing slurry of claim 18, wherein
the metal oxide abrasive is at least one compound selected from the
group consisting of including alumina, titania, zirconia, germania,
silica, ceria or mixture and chemical admixtures thereof.
20. The chemical mechanical polishing slurry of claim 19, wherein
the abrasive is a physical mixture of at least two elemental oxides
selected from the group consisting of alumina, titania, zirconia,
germania, silica, ceria.
21. The chemical mechanical polishing slurry of claim 16, wherein
the abrasive is milled or ground.
22. The chemical mechanical polishing slurry of claim 17, including
from about 2 to about 15 weight percent metal oxide abrasive.
23. The aqueous chemical mechanical polishing slurry of claim 17,
comprising from about 0.5 to about 10 weight percent nitrate salt,
from about 0.5 to about 10 weight percent carboxylic acid and from
about 0.5 to about 10 percent soluble cerium.
24. The aqueous chemical mechanical polishing slurry of claim 17
comprising from about 0.1 to about 3.0 weight percent acetic acid,
and from about 0.1 to about 4.0 weight percent ammonium cerium
nitrate wherein the slurry has a pH of from about 3.8 to about
5.5.
25. A chemical mechanical polishing slurry comprising from about 2
to about 15 weight percent metal oxide abrasive, from about 0.5 to
about 10 weight percent nitrate salt, from about 0.5 to about 10
weight percent carboxylic acid and from about 0.5 to about 10
percent soluble cerium, wherein the slurry has a pH of from about 3
to about 11.
26. The chemical mechanical polishing slurry of claim 25 comprising
from about 0.1 to about 3.0 weight percent acetic acid, from about
0.1 to about 4.0 weight percent ammonium cerium nitrate, and from
about 1.0 to about 15 percent fumed silica, wherein the slurry has
a pH from about 3.8 to about 5.5.
27. The chemical mechanical polishing slurry of claim 25 comprising
from about 0.1 to about 3.0 weight percent acetic acid, from about
0.1 to about 4.0 weight percent ammonium cerium nitrate, and from
about 1.0 to about 15 percent milled or ground ceria, wherein the
slurry has a pH from about 3.8 to about 5.5.
28. A method for removing at least a portion of a silicon dioxide
layer from a substrate comprising:
mixing a salt, a soluble cerium compound, a carboxylic acid, and
de-ionized water to form a chemical mechanical polishing
composition having a pH of from about 3.0 to about 11.0;
applying the chemical mechanical polishing composition to the
substrate; and
removing at least a portion of the silicon dioxide layer from the
substrate by bringing a pad into contact with the substrate and
moving the pad in relation to the substrate.
29. The method of claim 28, wherein the substrate is a layered
substrate comprising at least one layer of silicon dioxide and at
least one layer of silicon nitride.
30. The method of claim 29, wherein the silicon dioxide is removed
at a rate at least five-fold greater than the removal rate of
silicon nitride.
31. The method of claim 28, wherein the carboxylic acid is acetic
acid.
32. The method of claim 28, wherein the salt and soluble cerium
compound are ammonium cerium nitrate.
33. The method of claim 28, further including at least one metal
oxide abrasive selected from the group consisting of including
alumina, titania, zirconia, germania, silica, ceria and mixtures
thereof.
34. The method of claim 33, wherein the metal oxide abrasive is
silica.
35. A method for removing at least a portion of a silicon dioxide
layer from a silicon wafer, said silicon wafer including a silicon
nitride layer, said method comprising:
mixing from about 2 to about 15 weight percent silica, from about
0.1 to about 4.0 weight percent ammonium cerium nitrate, from about
0.1 to about 3.0 weight percent of acetic acid and de-ionized water
to form a chemical mechanical polishing slurry having a pH of
between about 3.8 to about 5.5;
applying the chemical mechanical polishing slurry to a pad;
rotating the pad; and
removing at least a portion of the silicon dioxide layer by
bringing the rotating pad into contact with the wafer and rotating
the wafer in relation to the rotating pad.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to chemical mechanical polishing
slurries for semiconductor integrated circuit substrates.
Specifically, this invention is a CMP slurry having a unique
chemistry that is especially suitable for chemical mechanical
planarization where a high silicon dioxide removal rate, and a low
silicon nitride removal rate are required on the same
substrate.
2. Description of the Related Art
Integrated circuits (IC) are made up of millions of active devices
formed in or on a silicon substrate. The active devices form
functional circuits and components. These devices are then
connected by the use of multilevel metallized interconnects and
vias. Interconnection structures normally have a first layer
metallization, an interconnect plug, a second layer of
metallization, and sometimes a third or more layers of
metallization with their respective interconnects. Inter level
dielectrics (ILDs), such as doped and undoped SiO2 are used to
electrically isolate the different levels of interconnections.
Shallow trench isolation (STI) is a technology for device isolation
in a give layer in the IC manufacturing process. In the STI
process, silicon nitride is deposited on thermally grown oxide.
After deposition of the nitride, a shallow trench is etched into
the substrate using a mask. A layer of oxide is then deposited into
the trench so that the trench forms an area of insulated dielectric
which acts to isolate the devices in a chip, and thus reduces the
cross-talk between active devices. The excess deposited oxide must
be polished of and the trench planarized to prepare for the next
level of metallization. The silicon nitride is applied to the
silicon to prevent polishing of the masked silicon oxide of the
device.
In a typical mechanical polishing process, the substrate is placed
in direct contact with a rotating polishing pad. A carrier applies
pressure against the backside of the substrate. During the
polishing process, the pad and table are rotated while a downward
force is maintained against the substrate back. An abrasive and
chemically reactive solution, commonly referred to as "a CMP
slurry", is flowed onto the pad during polishing. The chemicals and
abrasive particles in the slurry initiate the polishing process by
interacting with the wafer being polished. The polishing process is
facilitated by the rotational movement of the pad relative to the
substrate as slurry is provided to the wafer/pad interface.
Polishing is continued in this manner until the final desired film
thickness is achieved by removal of the required amount of
thin-film material.
When polishing oxides, it is desirable of the slurry used to have a
high removal rate towards the oxide layer and a low removal rate
towards other layers which may be exposed during CMP, such as
silicon nitride. The polishing slurry should be tailored to provide
effective polishing at the desired polishing ranges selective to
specific thin layer materials, while minimizing, at the same time,
surface imperfections, defect, corrosion, erosion and the removal
of silicon nitride and other stop layers.
CMP slurries useful for polishing oxides typically contain an
abrasive at an alkaline or high pH. These slurries either rely on
potassium hydroxide or ammonium hydroxide to effectively buffer the
high pH. While these slurries polish silica at high rates they also
polish silicon nitride at high rates. Typically, the ratio of these
removal rates, i.e., the selectivity is, at most, about 5 to 1
silicon oxide to silicon nitride. It is believed that the mechanism
of silicon nitride polishing is oxidative hydrolysis of the nitride
to the oxide in an aqueous environment. At alkaline pH this oxide
and nitride are similarly etched at a high rate. Thus, present CMP
slurries undesirably polish silicon nitride at an unacceptably high
rate.
There remains a need in the semiconductor industry for CMP slurries
that have greater than a 5 to 1 oxide to nitride selectivity.
Accordingly, new CMP slurries that selectively remove the oxide at
high rates while leaving the stop layer of silicon nitride
relatively intact are needed to overcome the present manufacturing
problems, increase throughput and reduce costs of the CMP process.
This is because a low selectivity process, when used in a
manufacturing environment, will necessarily suffer
overpolishing--in thinner film parts of the wafer--and the nitride
stop layer will not prevent breakthrough to the underlying thin
film(s).
SUMMARY OF THE INVENTION
This invention is a chemical mechanical polishing composition that
is capable of polishing a silicon dioxide layer at a high rate.
This invention is also a chemical mechanical polishing composition
that inhibits the polishing of a silicon nitride film.
In addition, this invention is a method of using a chemical
mechanical polishing composition that selectively removes silicon
dioxide from a substrate while leaving a silicon nitride layer
associated with the substrate essentially intact.
In one embodiment, this invention is a chemical mechanical
polishing composition comprising carboxylic acid, a salt and a
soluble cerium compound. The composition has a pH from about 3.0 to
about 11, and preferably from about 3.8 to about 5.5 and is useful
for selectively removing silicon dioxide from layered
substrates.
In another embodiment, this invention is a chemical mechanical
polishing slurry comprising the chemical mechanical polishing
composition described above and an abrasive. The slurry is
especially useful for silicon dioxide film polishing.
In still another embodiment, the present invention is a method for
using a chemical mechanical polishing composition comprising a
carboxylic acid, a salt and a soluble cerium compound in an aqueous
solution having a pH from about 3.0 to about 11 to selectively
remove oxide overfill in preference to a silicon nitride film layer
during the manufacture of integrated circuits and
semiconductors.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1--Plot of pH versus PETEOS removal rate and nitrate removal
rate.
DESCRIPTION OF THE CURRENT EMBODIMENTS
The present invention is directed to a chemical mechanical
polishing composition that comprises, a carboxylic acid, a salt,
and a soluble cerium compound, having a pH of from about 3.0 to
about 11.0. The chemical mechanical composition may be used alone
or it may be combined with a metal oxide abrasive to form a slurry.
The compositions and slurries of this invention polish oxide layers
such as silicon dioxide layers associated with substrates at high
rates. In addition, the compositions of this invention have been
found to inhibit silicon nitride polishing. The present invention
is also directed to novel methods for using the compositions and
slurries of this invention to polish oxide layers.
Before describing the details of the various preferred embodiments
of this invention a term that is used herein will be defined. The
"chemical mechanical composition" refers to the combination of at
least one carboxylic acid, at least one salt, and at least one
soluble cerium compound that may be used in conjunction with an
abrasive pad to remove one or more layers of a substrate. The term
"slurry" or "chemical mechanical polishing slurry" refers to the
combination of the chemical mechanical polishing composition and at
least one abrasive.
Carboxylic acids useful in a CMP slurry of the present invention
include monofunctional and di-functional carboxylic acids and their
salts. Preferably, the carboxylic acid is selected from the group
including acetic acid, adipic acid, butyric acid, capric acid,
caproic acid, caprylic acid, citric acid, glutaric acid, glycolic
acid, formic acid, fumaric acid, lactic acid, lauric acid, malic
acid, maleic acid, malonic acid, myristic acid, oxalic acid,
palmitic acid, phthalic acid, propionic acid, pyruvic acid, stearic
acid, succinic acid, tartaric acid, valeric acid,
2-(2-methyoxyethoxy) acetic acid, 2-[2-(2-methyoxyethoxy)ethyoxy]
acetic acid, poly(ethylene glycol)bis(carboxymethyl)ether, and
derivatives, including salts thereof. A most preferred carboxylic
acid is acetic acid.
In the composition of the present invention, the carboxylic acid
can comprise greater than 10% of the slurry. In a preferred
embodiment, the carboxylic acid is present in the composition of
this invention in an amount ranging from about 0.05 to about 10% by
weight. In a more preferred embodiment, however, the carboxylic
acid is present in the composition of this invention in an amount
ranging from about 0.1 to about 3%.
The chemical mechanical composition of the present invention
includes a salt. The term "salt" refers to any water soluble salts
including organic salts and inorganic salts such as nitrate,
phosphate, and sulfate salts. Soluble salts also refers to salts
that are only partially or marginally soluble in water. Preferred
salts are nitrate salts.
The term "nitrate salt" includes nitric acid. Useful nitrate salts
include compositions of the formula (M).sub.n (NO.sub.3).sub.m
where n and m are both integers. When n=m, M is monovalent and can
be alkali earth metals such as Li, Na, K, as well as H, NH.sub.4,
NR.sub.4 where R is an alkyl group having from 1 to 10 or more
carbon atoms or is a mixture thereof, including NMe.sub.4,
NBu.sub.4 and so forth. When n.noteq.m, then M is a multivalent
cation or metal or a combination of a multivalent cations and
monovalent cations. One known preferred nitrate salt is ammonium
cerium nitrate, (NH.sub.4).sub.2 Ce(NO.sub.3).sub.6.
The salt may be present in the composition in the amount of from
about 0.05 to about 6% by weight of the composition. It is most
preferred that the salt is present in the composition in the amount
ranging from about 0.1 to about 4% by weight.
The chemical mechanical composition of the present invention
includes at least one soluble cerium compound. Non-limiting
examples of soluble cerium compounds useful in a composition of the
present invention include water soluble hydrated and non-hydrated
salts of cerium hydroxide (Ce(OH).sub.4), ammonium cerium sulfate,
(NH.sub.4).sub.2 SO.sub.4 Ce.sub.2 (SO.sub.4).sub.3 ; cerium
acetate, Ce(O.sub.2 CH.sub.3).sub.3 ; cerium sulfate,
Ce(SO.sub.4).sub.2 ; cerium bromate, Ce(BrO.sub.3).sub.3
.multidot.9H.sub.2 O; cerium bromide, CeBr.sub.3 ; cerium
carbonate, Ce(CO.sub.3).sub.2, cerium chloride, CeCl.sub.3 ; cerium
oxalate, Ce(C.sub.2 O.sub.4).sub.3 ; cerium nitrate,
Ce(NO.sub.3).sub.3 (OH).multidot.6H.sub.2 O and any other known
soluble cerium compounds. A preferred soluble cerium compound is
ammonium cerium nitrate, (NH.sub.4).sub.2 Ce(NO.sub.3).sub.6. The
soluble cerium compound will be present in the composition of this
invention in an amount ranging from about 0.05 weight percent to
about 10.0 weight percent and preferably from about 0.1 to about
4.0 weight percent.
A preferred embodiment of the chemical mechanical composition of
the present invention includes ammonium cerium nitrate as both the
salt and as the soluble cerium compound. Other soluble cerium
nitrate salts may be incorporated into the composition of this
invention as both the soluble cerium compound and as the salt.
Ammonium cerium nitrate may be present in composition of the
present invention in an amount ranging from about 0.05 to about 6%
weight percent of the overall composition weight. A more preferred
range of ammonium cerium nitrate is from about 0.1 to about 4.0
weight percent.
The chemical mechanical composition of this invention may be used
alone or in conjunction with an abrasive to give a chemical
mechanical polishing "slurry."Abrasives useful in conjunction with
the compositions of the present invention include metal oxide
abrasives. The metal oxide abrasive may be selected from the group
including alumina, titania, zirconia, germania, silica, ceria and
mixtures thereof. In addition, useful abrasives may be the result
of mixing precursers of two or more metal oxides to give a chemical
admixture of a mixed metal oxide abrasive. For example, alumina can
be co-formed with silica, or combined alumina/silica.
Useful metal oxide abrasives may be produced by any techniques
known to those skilled in the art, including high temperature
processes such as sol-gel, hydrothermal or, plasma process, or by
processes for manufacturing fumed or precipitated metal oxides.
Pulverized or crushed metal oxide abrasives are also useful in the
CMP slurry of this invention and may be manufactured by milling or
grinding using conventional manufacturing techniques such as
jet-milling, ball milling, bead milling, and other milling and
pulvizeration techniques and process know to one skilled in the
art.
Preferred abrasives suitable for the CMP slurries of this invention
are silica and cerium oxide (ceria) with fumed silica being most
preferred. Other suitable silica abrasives can be made by methods
such as sol-gel, hydrothermal, plasma process, flame pyrolysis or
by other processes for manufacturing metal oxides.
Pulverized abrasives are also suitable for this invention. Any
pulverized metal oxide abrasive may be used in a CMP slurry of this
invention. However, pulverized cerium oxide is preferred. The
cerium oxide abrasive is ground in a media mill to give pulverized
ceria. The original cerium oxide particle may be either mined
cerium oxide or precipitated and calcined cerium oxide or a
combination thereof. The grinding may be accomplished in an aqueous
medium using any type of a grinding or milling apparatus such as by
jet milling or ball milling. A preferred grinding mechanism is a
medial mill with either yttria tetragonal zirconia (YTZ) or
zirconium silicate media. The grinding process may use a dispersant
or steric stabilizer.
The preferred pulverized metal oxide abrasive will have a narrow
particle size distribution with a median particle size (i.e.,
aggregate particle or single particle) of less than about 0.5
microns. The particles may be diluted and filtered after the
grinding. Preferably, after filtration, the particle sizes of the
pulverized metal oxide abrasive range from about 40 to about 1000
nm, and preferably from about 100 to about 300 nm. The preferred
pulverized abrasive should contain less than about 10 weight
percent of particles having a median particle size greater than 0.6
.mu.m.
Precipitated cerium oxide is a suitable abrasive for oxide CMP.
Precipitated cerium oxide particles are made from a variety of
precursors including acetates, carbonates and hydroxide and nitrate
salts of cerium. The median particle size of precipitated cerium
oxide particles may range of from about 10 nm to about 500 nm, with
the preferred size of precipitated cerium oxide particles being in
the range of from about 30 to about 300 nm.
Another preferred abrasive is fumed silica. The production of fumed
metal oxides is a well-known process which involves the hydrolysis
of suitable feed stock vapor (such as silicon tetrachloride for a
silica abrasive) in a flame of hydrogen and oxygen. Molten
particles of roughly spherical shape are formed in the combustion
process. The diameters of the particles are varied through process
parameters, and these molten spheres of silica or similar oxide,
typically referred to as primary particles, fuse with one another
by colliding at their contact points to form branched, three
dimensional chain-like aggregates. The force necessary to break
aggregates is considerable and often irreversible. During cooling
and collecting, the aggregates undergo further collisions that may
result in some mechanical entanglement causing the formation of
aggregates.
A preferred metal oxide will have a surface area, as calculated
from the method of S. Brunauer, P. H. Emmet, and I. Teller, J. Am.
Chemical Society, Volume 60, Page 309 (1938) and commonly referred
to a BET, ranging from about 5 m.sup.2 /g to about 430 m.sup.2 /g
and preferably from about 30 m.sup.2 /g to about 170 m.sup.2 /g.
Due to stringent purity requirements in the IC industry the
preferred metal oxide should be of a high purity. High purity means
that the total impurity content, from sources such as raw material
impurities and trace processing contaminants, is typically less
than 1% and preferably less than 0.01% (i.e., 100 ppm).
In a preferred embodiment, the metal oxide abrasive consists of
metal oxide aggregates having about 99 weight percent of the
particles less than about 1.0 micron in diameter, a mean aggregate
diameter less than about 0.4 micron and a force sufficient to repel
and overcome the van der Waals forces between abrasive aggregates
themselves. Such metal oxide abrasives have been effective in
minimizing or avoiding scratching, pit marks, divots and other
surface imperfections during polishing. The aggregate size
distribution in the present invention may be determined using known
techniques such as transmission electron microscopy (TEM). The mean
aggregate diameter refers to the average equivalent spherical
diameter when using TEM image analysis, i.e., based on the
cross-sectional area of the aggregate. The surface potential or the
hydration force of the metal oxide particles must be sufficient to
repel and overcome the van der Waals attractive forces between the
particles.
In another preferred embodiment, the metal oxide abrasive may
consist of discrete metal oxide particles having a particle
diameter less than 0.5 micron (500 nm) and a surface area ranging
from about 10 m.sup.2 /g to about 250 m.sup.2 /g.
A CMP slurry of this invention will include from about 2 weight
percent to about 25 weight percent metal oxide abrasive and
preferably from about 2 weight percent to about 15 weight percent
metal oxide abrasive.
Metal oxide abrasives useful in CMP slurries of the present
invention are incorporated into the aqueous medium of the polishing
slurry as a concentrated aqueous dispersion of metal oxides
comprising from about about 3% to about 55% solids, and preferably
between 30% and 50% solids. The aqueous dispersion of metal oxides
may be produced using conventional techniques, such as slowly
adding the metal oxide abrasive to an appropriate media, for
example, de-ionized water, to form a colloidal dispersion. The
dispersions are typically completed by subjecting them to high
shear mixing conditions known to those skilled in the art.
The abrasives useful in a CMP slurry of the present invention can
be a mixture of the abrasives described above. For example,
precipitated cerium oxide, pulverized cerium oxide (also referred
to a ceria) and fumed silica could be incorporated into a CMP
slurry of the present invention. Other combinations of abrasives
are also useful in the CMP slurry. In addition, the mixture of
abrasives could include any relative proportion of one abrasive to
another. For example, a combination of from about 5 to 100 weight
percent of the pulverized oxide abrasive described above with from
about 0 to about 95 weight percent precipitated abrasive has been
found to be effective as a CMP slurry abrasive in STI
applications.
Commercially available precipitated cerium oxides sold at a pH of
about 1.5, are ineffective as CMP slurries. We have, however,
discovered that significantly increasing the pH of the commercially
available slurry to about 3.5 results in a CMP slurry that is
useful for STI polishing. Furthermore, we have surprisingly
discovered that a CMP slurry with the composition and pH disclosed
above exhibits a high oxide layer removal rate and low nitride
layer removal rate.
The CMP slurry of this invention must have a pH from about 3.0 to
about 11.0 to be effective. More preferably, the slurry pH will
range from about 3.5 to about 6.0, and most preferably the pH is
from about 3.8 to about 5.5. Slurry pH is adjusted by adding any
base to the composition and preferably by adding a non-metal base
such as ammonium hydroxide to the slurry.
In order to further stabilize a polishing slurry of this invention
against settling, flocculation and decomposition of the oxidizing
agent, a variety of additional optional additives, such as
surfactants, polymeric stabilizers or other surface active
dispersing agents, can be used. The surfactant can be anionic,
cationic, nonionic, amphoteric and combinations of two or more
surfactants can be employed. Furthermore, it has been found that
the addition of a surfactant may be useful to improve the
within-wafer-non-uniformity (WIWNU) of the wafers, thereby
improving the surface of the wafer and reducing wafer defects.
In general, the amount of an additive used, such as a surfactant,
in the present invention should be sufficient to achieve effective
steric stabilization of the slurry and will typically vary
depending on the particular surfactant selected and the nature of
the surface of the metal oxide abrasive. For example, if not enough
of a selected surfactant is used, it will have little or no effect
on stabilization. On the other hand, too much of the surfactant may
result in undesirable foaming and/or flocculation in the slurry. As
a result, additives like surfactants should generally be present in
a range between about 0.001% and 10% by weight. Furthermore, the
additive may be added directly to the slurry or treated onto the
surface of the metal oxide abrasive utilizing known techniques. In
either case, the amount of additive is adjusted to achieve the
desired concentration in the polishing slurry.
The chemical mechanical polishing compositions and slurries of this
invention are capable of selectively removing the silicon dioxide
layer from layered substrates at very high rates. Furthermore, the
compositions and slurries of this invention inhibit the polishing
of silicon nitride from layered substrates. One important
application for the chemical mechanical polishing compositions and
slurries of this invention is in the manufacture of integrated
circuits and semiconductors. In such a polishing application, the
compositions and slurries of this invention effectively remove
silicon dioxide for shallow trench device isolation.
The compositions and slurries of this invention preferably exhibit
oxide removal rate of from about 1200 .ANG./min to about 6000
.ANG./min or more with an oxide to nitride removal selectivity of
from about 5 to about 100 or more and preferably from about 15 to
about 50 or more.
The compositions and slurries of the present invention may be
incorporated in a single package which includes an aqueous
composition of at least one carboxylic acid, a soluble cerium
compound, a salt, an optional abrasive, and optional additives at
the requisite pH. To avoid changes in activity of slurry over time
it may be preferable to use at least a two package system where the
first package comprises at least one carboxylic acid, a salt and a
soluble cerium compound at any pH and the second package comprises
the optional abrasive at any pH. These two packages will be
engineered so that when they are mixed, the useful composition is
in the required pH range. Alternatively, the components in one
container may be in dry form while the component in the other
container are in the form of an aqueous dispersion. Other
two-container combinations of the ingredients of the CMP slurry of
this invention are within the knowledge of one having ordinary
skill in the area.
At the requisite pH, the compositions and slurries of the present
invention do not significantly increase the silicon nitride removal
rate. However, the composition and slurry of this invention
significantly increases the removal rate of silicon dioxide in
comparison to known slurries. The polishing slurry of the present
invention may be used during the various stages of semiconductor
integrated circuit manufacture to provide effective removal of
silicon oxide layers at desired removal rates while minimizing
surface imperfections and defects.
EXAMPLE 1
The following examples illustrate preferred embodiments of this
invention as well as preferred methods for using compositions of
this invention. All compositions and slurries were used in an STI
polishing protocol as outlined below.
The CMP slurries were used to chemically-mechanically polish
blanket PETEOS and silicon nitride using a IC1000/SUBA IV pad stack
manufactured by Rodel, Inc. The polishing was performed using an
IPEC/WESTECH 472 CMP tool at a down force of 9 psi, a slurry flow
rate of 140 ml/min., a platen speed of 35 rpm and a carrier speed
of 24 rpm.
EXAMPLE 2
Pulverized Ceria Formulations
A pulverized ceria slurry was prepared in order to evaluate its
ability to polish blanket silicon dioxide and nitride wafers.
Rhodite grade 400HS ceria, having particle sizes approximately 2-4
.mu.m was purchased from Universal Photonics, Hicksville, N.Y. and
pulverized using an agitator bead mill to a primary median particle
size of 150 nm. Pulverizing was accomplish under wet conditions so
that the resulting slurry, pH approximately 7.5-8.5, contained
20-30% solids after the pulverizing process.
The slurry was then diluted and the pH adjusted to produce the
slurries listed in Table 1. The slurries were used to polish a
substrate according to the methods described in Example 1.
TABLE 1 ______________________________________ PETEOS RR Nitride RR
Slurry No. pH % solids (.ANG./min) (.ANG./min) Selectivity
______________________________________ 1 8 4.0 925 1050 0.89 2 8
5.0 4337 1137 3.81 3 8 7.5 4800 1130 4.25 4 8 10.0 5145 1153 4.46 5
10 4.0 4342 1101 3.95 6 10 10.0 4344 1015 4.28
______________________________________
The pulverized ceria slurries were used for polishing The data
indicates that the pulverized ceria slurries yield very high PETEOS
(silicon oxide layer) removal rates.
EXAMPLE 3
Precipitated Ceria Nitrate Formulations
A nitrate stabilized ceria slurry containing precipitated ceria
particles, nitric acid, acetic acid, pH=1.8 and 20% solids, was
purchased from Nyacol Products (Ashland, Mass.). The pH of the
slurry was adjusted to from about 4.2-6.8 by adding ammonium
hydroxide. The slurries were used to polish substrates according to
the method described in Example 1. The polishing results are
reported in Table 2.
TABLE 2 ______________________________________ Slurry % PETEOS
Nitride No. pH solids Additives RR RR Selectivity
______________________________________ 7 4.2 20 406 14.5 28 8 5.8
20 281 208 1.35 9 6.1 20 241 281 0.86 10 6.2 20 163 354 0.46
______________________________________
The polishing data indicates that at the lowest pH (4.2)
selectivity is high, but overall oxide removal rates are low.
EXAMPLE 4
Precipitated Ceria Acetate Formulations
A ceria acetate slurry, containing ceria particles and acetic acid,
pH=1.8 and 20% solids, was purchased from Nyacol Products (Ashland,
Mass.). The pH of the slurry was adjusted to 4.5 and the solids
content to 15%. The slurry was applied to substrate according to
the methods described in Example 1 and the result showed an oxide
layer removal rate of 117 .ANG./min and a nitride layer removal
rate of 10.5 .ANG./min for an oxide to nitride selectivity of
11.1.
EXAMPLE 5
Crushed/Precipitated Ceria Formulations
A ceria slurry, composed of varying weight percent amounts of the
pulverized ceria manufactured as set forth in Example 2 and
precipitated ceria purchased from Nyacol Products (Ashland, Mass.)
was formulated as shown in Table 3. The slurries were used to
polish substrates according to the methods described in Example 1
and the polishing results are set forth in Table 3, below.
TABLE 3 ______________________________________ PETEOS Nitride
Slurry % total % pulverized RR RR No. pH solids ceria in slurry
(.ANG./min) (.ANG./min) Selectivity
______________________________________ 11 4 8 20 1595 108.4 14.71
12 4 8 40 2168 183.4 11.82 13 4 8 60 3356 826.5 4.06 14 4 8 80 4785
209.1 22.88 ______________________________________
The results indicate that a CMP slurry including 80% pulverized
ceria and 20% precipitated ceria produced the most desired
properties of high PETEOS rates, low nitride rates and high
selectivity.
EXAMPLE 6
Chemical Formulation Using Pulverized Ceria
A slurry, composed of L-90, a fumed silica particles manufactured
by Cabot Corporation and sold under the trademark CAB-O-SIL.RTM.,
ammonium cerium nitrate, acetic acid, of varying percentages, and
deionized water was formulated as shown in Table 4. All slurries
were adjusted to pH=4 after the inclusion of additives. The
slurries were applied to substrate according to the methods
described in Example 1.
TABLE 4 ______________________________________ weight weight % Amm.
% Nitride PETEOS weight % Cerium Acetic RR RR Selec- Slurry silica
Nitrate Acid (.ANG./min) (.ANG./min) tivity
______________________________________ 20 4 0.1 0.1 58 280 4.83 21
4 0.1 1 52 253 4.87 22 4 0.65 0.5 59 619 10.49 23 4 1 0.1 44 1535
34.89 24 4 1 1 312 1524 4.88 25 4 1 0 104.62 1337.9 12.79 26 4 2
0.05 57.51 1103 19.18 27 4 3 0.1 89.99 835.8 9.29 28 4 1 0.5 71.5
803.1 11.23 29 4 2 0.1 24.1 346.6 14.38 30 4 2 0.5 71.1 768.0 10.8
______________________________________
High PETEOS removal rates and low nitride removal rates were
obtained with high nitrate (1% nitrate) content and low (0.1%)
acetic acid content.
EXAMPLE 7
Chemical Formulation Using Silica--pH Test
A slurry, composed of 4 weight percent CAB-O-SIL.RTM. L-90 fumed
silica, 1.8 weight percent ammonium cerium nitrate, and 0.6 weight
percent acetic acid of varying percentages was formulated as shown
in Table 5. The pH of the slurries varied from between 4.0 to 5.0.
The slurries were applied to substrate according to the methods
described in Example 1.
TABLE 5 ______________________________________ weight weight %
Acetic PETEOS Slurry % silica pH Acid Nitride RR RR Selectivity
______________________________________ 31 4 4.0 0.6 114 1713.7
15.03 32 4 4.3 0.6 141 1988.9 14.11 33 4 4.7 0.6 199 2810.5 14.12
34 4 5.0 0.6 219 2355 10.75
______________________________________
High PETEOS removal rates are obtained and selectivity was very
good for each slurry. The results indicate that slurry pH has a
strong effect on PETEOS removal rate and the optimum removal rate
of oxide is achieved at about pH 4.7 (FIG. 1).
While the present invention has been described by means of specific
embodiments, it will be understood that modifications may be made
without departing from the spirit of the invention. The scope of
the invention is not considered to be limited by the description of
the invention set forth in the specification and examples, but
rather defined by the following claims.
EXAMPLE 8
A composition composed of 1.8 wt % ammonium cerium nitrate, 0.8 wt
% acetic acid, and deionized water was used to polish PETEOS and
silicon nitride wafers according to the method of Example 1. The pH
of the slurry was adjusted to 4.5. The composition polished PETEOS
at 690 .ANG./min and silicon nitride at 23 .ANG./min, giving a
PETEOS selectivity of 30.
* * * * *